Thermal Behaviour and Thermokinetic Studies of Co(II), Ni(II), Cu(II) and
Cd(II) 1,2,4-Triazole-3-Thione Schiff Bases Complexes
M.A.El-Gahami, S.A.El-Gyar, A. Abd El-Sameh and S.A.Ibrahim
Chemistry Department, Faculty of Science, Assiut University, Assiut, Egypt.
Email: elgahami@yahoo.com
1,2,4-triazole-3-thiones Schiff bases and their complexes have been reported to be
biologically versatile compounds having bactericidal properties(1-3).
A series of complexes of 1,2,4-triazole-3-thione Schiff bases with Co(II) Ni(II),
Cu(II)and Cd(II) ions have been prepared according to procedure reported in the literature(4).
The structure of the complexes was determined by means of elemental analysis, molar
conductance, magnetic measurements, infrared and electronic spectral data and thermal
studies(4). The thermal decomposition study of Co(II), Ni(II), Cu(II) and Cd(II) complexes
was monitored by TG, DTG and DTA analysis in dynamic atmosphere of nitrogen. The
thermal degradation takes place in three to five steps depending on the metal ion present. The
decomposition course and steps were analyzed and the kinetic parameters: order of the
decomposition reaction (n), correlation coefficient (r), activation energy (E) and preexponential factor (collision factor) (Z) of the non-isothermal decomposition steps were
computed using Coats-Redfern(5) and Horowitz-Metzger(6) methods and discussed.
Comparison of the two sets of kinetic parameters shows that deviation between them is not so
great, considering the approximations involved in the Horowitz-Metzger method.
Thermodynamic parameters: entropy (S#), enthalpy (H#) and Gibbs free energy (G#) of
activation, were calculated using a standard relations(7) and discussed. The dehydration
stability of the complexes increases in the order (Cu Ni Co) is in accordance with both
Irving-Williams order(8) and the ionic volume of the metal ions(9). The activation energies of
the thermal degradation steps lie in the range 0.7-70.61 KJmol-1.
Fig.1. TG-DTG curves of [Cu(ABT)2 2H2O]Cl2
(nitrogen atmosphere)
Fig.2. Relationships between the initial dehydration temperature
or activation energy and metal ion type of ABT complexes
Fig3: Horowitz-Metzger plots for the three decomposition steps
Cu(ABT)2 2H2O]Cl2 a) first step b) second step c) third step.
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